Re: Misaligned accesses with MS ARM compiler

From: Alan Gillespie (agillesp_at_qualcomm.com)
Date: 04/28/04 

Date: Wed, 28 Apr 2004 18:39:21 +0100

Thanks to everyone who responded, and apologies to Michael for doubting his word. This is exactly what I need.

Shows what you get for relying on free documentation. Are there any other gems like this that are worth knowing about?

--Alan Gillespie.

"Paul G. Tobey [eMVP]" <ptobey_no_spam@instrument_no_spam.com> wrote in message
news:eXbRDCULEHA.2396@TK2MSFTNGP12.phx.gbl...
> It works, though. It's defined in winnt.h.
>
> It will change the code generated for the item so that it is accessed as an
> array of two or four bytes, which will then be reassembled in a register and
> used as a WORD or DWORD.
>
> Paul T.
>
> "Alan Gillespie" <agillesp@qualcomm.com> wrote in message
> news:%23Us3D8TLEHA.4080@TK2MSFTNGP12.phx.gbl...
> > At the risk of appearing ignorant - you are talking about the MS ARM
> compiler as included with eVC4, aren't you? As in
> > clarm.exe (I have version 12.20.9615)?
> >
> > I just looked at the compiler documentation and couldn't find any mention
> of UNALIGNED of __unaligned anywhere.
> >
> > --Alan Gillespie.
> >
> >
> > "Michael J. Salamone [eMVP]" <mikesa#at#entrek#dot#com> wrote in message
> news:ug8WSkTLEHA.1264@TK2MSFTNGP12.phx.gbl...
> > > Use UNALIGNED in your declararation - which resolves to __unaligned
> keyword.
> > >
> > > --
> > >
> > > Michael Salamone [eMVP]
> > > Entrek Software, Inc.
> > > www.entrek.com
> > >
> > >
> > >
> > > "Alan Gillespie" <agillesp@qualcomm.com> wrote in message
> > > news:e1TOPcTLEHA.1272@tk2msftngp13.phx.gbl...
> > > >
> > > > Does anyone know of a way to tell the ARM compiler that a WORD or
> DWORD
> > > pointer addresses an object that is not (or
> > > > might not be) aligned on a 16 or 32 bit boundary?
> > > >
> > > > Effectively what I want to do is this:
> > > >
> > > > BYTE *pBuffer = malloc(something);
> > > > WORD *pWord = (WORD *) &pBuffer[arbitrary_offset];
> > > > DWORD *pDWord = (DWORD *) &pBuffer[another_arbitrary_offset];
> > > >
> > > > *pWord = word_value; /* May be misaligned */
> > > > *pDWord = dword_value; /* May be misaligned */
> > > >
> > > > I have tried various versions of #pragma pack() without success. I
> could,
> > > of course, use WORD and DWORD temporaries and
> > > > memcpy() into the array but that is messy. There are other, equally
> messy,
> > > workarounds involving byte manipulation.
> > > >
> > > > The problem arises because I am porting a large amount of code that
> was
> > > written for the ARM ADS compiler, which has such
> > > > a facility.
> > > >
> > > > Thanks,
> > > > --Alan Gillespie.
> > > >
> > > >
> > >
> > >
> >
> >
>
>